The risk of tuberculosis in a person who has been in contact with a tuberculosis patient depends on several factors.

There are several forms of tuberculosis, but only the respiratory forms are contagious. The inhalation of tuberculous bacillae increases in cases of close, frequent or prolonged exposure. In over 80% of cases, tuberculous infection does not develop into tuberculosis. Tuberculosis generally occurs within 2 years of exposure to a contagious patient. This risk is higher in some people, especially children under the age of 5 and immunocompromised patients (those infected with HIV in particular).

Exposed persons should be examined for clinical signs and symptoms of pulmonary tuberculosis: cough, fatigue, fever, night sweats, weight loss; with the addition of a chest x-ray.

Tests, such as the TST (tuberculin skin test) and IGRA (interferon gamma release assays) are not decisive in identifying a risk of tuberculosis after exposure.

In the case of minimal risk, there is no need for prophylactic treatment or special monitoring. When infection is likely, it is reasonable not to start treatment but to offer clinical and x-ray monitoring 3 months, 1 year and 2 years after exposure. This strategy makes it possible to treat people developing tuberculosis as early as possible while avoiding the sometimes severe adverse effects of prophylaxis. When there is a high risk of the disease developing, a prophylactic treatment is justified, either with isoniazide alone for 6 months or combined with rifampicine for 3 months. These drugs carry the risk of drug interactions and of severe liver damage, and require close monitoring.

©Prescrire 1 November 2012

"Contacts of infectious tuberculosis patients. Monitor patients at highest risk of developing tuberculosis" Prescrire Int 2012; 21 (132): 270-275. (Pdf, subscribers only).